IMMUNE SUPPRESSIVE VIRUS-LIKE PARTICLES IN A DROSOPHILA PARASITOID - SIGNIFICANCE OF THEIR INTRASPECIFIC MORPHOLOGICAL VARIATIONS

The Eucoilid parasitoid Leptopilina boulardi is able to suppress its h ost Drosophila melanogaster immune reaction. Some strains, however, ar e non-immune suppressive to that host. Virus-like particles (VLPs) res ponsible for the immune suppressive ability were investigated in diffe rent strains of L. boulardi with histochemical and ultrastructural tec hniques. Membrane-bound particles containing vesicles were observed in the reservoir of the long gland and also in the egg canal of the ovip ositor. These particles are homologous with the immune suppressive VLP s already described in the reservoir of L. heterotoma. Similarities we re also observed with the L2 particles described previously around the chorion of the parasitoid egg after infestation. A weak positive DNA specific histochemical reaction was observed inside the reservoir and at the ultrastructural level. Feulgen-derived techniques demonstrated that the reaction was localized inside the particles. The morphology o f the particles as well as the immune suppressive ability varied betwe en strains. Two morphotypes of VLPs are described; the 'Is' morphotype (always observed in immune suppressive or Is strains) and the 'NIs' m orphotype (observed in the non-immune suppressive or NIs strain). The hybrids between Is and NIs strains produce a third type of particle, t he 'HIs' morphotype with half-immune suppressive ability and intermedi ate morphology. The origin of the particles' immune suppressive activi ty against D. melanogaster is discussed within the scope of host speci ficity.